Gas tube input circuit



July 15, 1952 J. KuRsHAN GAS TUBE INPUT CIRCUIT 2 SHEETS-SHEET 1 Filed March 30, 1.951

. Z a. w v 0 Mm I 5 a 2 a 7 l Hle o O 4. 6 a 7/ 4 W Ur, /f Il., Hm )MTV y, w #ST N s INVENTOR Jerome zms'bm l ATTORNEY July 15, 1952 J. KuRsHAN GAS TUBE INPUT CIRCUIT Filed March 50, 1951 ze s 32 ZSI-IEETS-SliEETZ T ram/rf BYMQMJA.

ATTCRNEY 'moreffofkthe main tube electrodes.

Patented .uly 115, 16952 Radio Corporation. of

of Delaware America, af'corporation Application March 3o, 1951', semaine; 218,299(

This invention relates to improvements -invr gaseous electron tube circuits, and particularly wan-improved circuit for'operating a gas filledV electron `tube of the type wherein the functions o'fl-ionizin'gythe tube gas and ofA passing current thrugh-theionizedigas are separated. Y

`rIn'a copendi-ng application' of E.'O. Johnson, Serial 4I"Io.185,74.'.5, led lSeptember 20, 1950, and assigned to the-assignee of the presentinvention, there is described a gas iilled electrontube in which# space charge neutralizing ions are generated bylan auxiliary ionizing discharge of electrosbetweenanauxiliary emitterl and one-or With this arrangement, .two very important advantages, are attained.- .l

First,`itfis found that very high current can be kpassed between the main emitter and collector-electrodes at potentials. far below those required-toionize the gas. Second', it is found that the-currentcfiowlbetween main emitter and col-r lector .can be controlled in variousV ways, one of Whichis'fby means of .a control electrode simliar toithat .used ,in the conventional vacuum tube.

For simplicity, gas Vtubes of. the typejust de,- scribeda'rereferred to herein as separated func-'- tionfigas'tubesi Whiletli'e separated function gas tuber'has beenV found :.very .useful for many applications, it has` one.characteristicgthat causes difficulty in some cases. Itihas been found thatthe grid-voltage plate-currentcharacteristic is not entirely linear. Consequently, high iidelityrreproduction'of input signals -isnot always, attainable with the Ycircuits heretofore `proposed for operating separated func-.- tiongastubes.

i2 Claims.v v(o1. 315-;349)

' referred to as thegrid-voltage ygridacteristic Vis' nonlinearr- Furthermore, the nonlinearity ofthe grid-voltagegrid-current char`A acteristic ycan' be reliedu on to coni'pensateinlarge measureY for l the nonlinearity the; gridvoltage plate-current character'ist-ici g v Y By 'providing a relativelyhigh impedance in the grid input circuitgthe grid voltage can be made to follow the applied signal voltage in a nonlinear manner so as to attain the desiredY linear relation between 4signal input and signal output. In accordance with a furtherl feature ofthe invention, if the linearizing gridcircuit impedance also is' made nonlinear, still`v further linearization of overall circuit yoperation can-be attained. f y i Y- f A more complete understanding of the invention can be had by reference to the following description of illustrative embodiments thereof, when considered in connection with the accompanying drawing, wherein Y -i vFig.= 1 is a view in cross-section of a typical tube such as may be used in accordance with they present invention,

Fig. 2 showsa typical grid-voltage plate-current characteristic curve for a tube of the type shown in Fig. 1, Y

Fig. .3 shows a typical grid-voltage grid-current characteristic curve for a tube such as is `shown inFigQl, l f

Fig. 4 is a schematic diagram showing inigen-f 6 eral form a separated function gas tube icircuit 1t;,is, ;therefore, one object of the present invention to provide an improved circuit for operating a separated function gas tube so as toY permit theuse of such tubes as high fidelity signal amplifiers." Y n y, y

yfurtherobject of the inventionfis to provide a,:separatedYl function gas tube energizing circuit which--fwill^overcome nonlinearityin the grid- 4plate-current vcharacteristics of such ancevwithfthe invention, the foreer related objects and advantages A afcircuit` wherein y*advantage is take. ,.foiftli.. nonlinear grido-voltage sridrcurrsllt' Characteristic of tnefseparated ,functQn .gasftube Duringfroperation, ion currentwill iiowjto a negatively biased control grid in a separated yfunction gas tube. Ithas beentfound Athat the` curverelati' th's'ion current' to the grid voltage (herein 1J,... ...ag

arranged in accordance with the invention,

iFig. k5 is a circuitr diagram showing one specifi embodiment of the present invention, Fig. Gushows the ,relation between signal input andsignal output voltageattainable'with a circuit such as is shown in Fig. 5, r x-4 Y .Fig.,7isa circuit diagram of a second `specific embodimentrofgthe present invention, f x

, Fig. 8 shows the current-voltage curve vof a non-llinear impedance element, FgS9-, 10 ,and llare circuit diagrams showing furtherr embodiments ofgthe invention.- Referring to.1ig.1,of.the drawing, there is shown in cross-section a@ Yseparated functionA gasA tube o ,fmthe type morenfully described and claimed in the above-mentioned copending applicationA of Johnson. In Fig. l, a gas'ptightenvelope I0 is provided with a cathode I2.;` A'U-shapedcontrol electrode. or grid I4 *and` a U-shapedanode, I6 partially surroundl the cathode l2. The gridild comprises a plurality of vparallel 'wires i5 which are supportedinspaced relation. The anode 'i6` may-be asheetmetalelement.Y` i fr' current char- Opposite the open ends of the grid I4 and the anode I6 there is mounted a cylindrical focusing electrode I8 provided with an elongated slot 20 facing the open ends of the grid and anode structures. An auxiliary cathode 22 is mounted coaxially within the focusing electrode I8.

A tube having a structure such as that shown inV Fig. 1 can be operated as follows:

If a voltage greater than the ionizing voltage of the gas in the tube is applied between the auxiliary cathode 22 and main cathode I2, an electron current will ow which will ionize the gas in the tube. As a result, a highly conduc-f tive mixture or plasma of ions and electronswill be created within the tube envelope. The fo- 4 cussion of Fig. 1. Between the anode I6 and the main cathode I2, there is connected a load circuit 24 in series with an operating voltage source. shown as a battery 26. Between the main cathode I2 and the auxiliary cathode 22 there is connected a source of ionizing voltage, shown as a battery 28, inseries with Yagcurrentlimiting resistor 30. The shield electrode I8 is :connected to the auxiliary electrode 22.

As thus far described, the circuit shown in Fig. 4 is, in general, similar to circuits such as conventionally are used with a separated function gas tube. In the usual case, a control voltage applied between the control grid I4 and the main cathode I2 would determine the current flow be- Y tween the maincathode I2 and anode I6 and,

tain high plasma densities with Very-"small amounts of current or power. With the tube gas ionized to createIplasma `in the manner just de. scribed, it becomes possible to pass a relatively highfcurrent between the main cathode andthe mainnanode with -a Avoltage dropwhich may be of-'theorder of 0.1 volt or less. Furthermore, itA

becomes possible to control :this main .cathode-` anode current by meansof the control electrode I4'fdisposed in the space -path as shown.-V

hence, through the load circuit 24.

' areV given hereinafter. The signal sourceSZ-visA Asjwas previously stated,A one ofthe diiiiculties Y encountered with the tube shownrinFig. l arisesA from lnonlinearity of the grid-Voltageplate-cur-J rent' characteristic. This vis illustrated by the curve'shown in Fig.l v2, which may be regarded as generally typicalof such tubes. FromFig. `2, it can be seenV that an incremental grid `voltage change in the vicinity of the 15 volt point on the chart will produce'a much smallervchange of platevcurrent than would an equalchange in the vicinity of, say, theV 5 volt point. For vsome applicationsthis is of little consequence, and would even be advantageous in a control system,V

characteristic isV overcome by taking' advantageof the somewhat similar nonlinearity. of the` grid-voltage grid-current characteristic.'

Asi is shOWnin'Fg'. 3, forexample',l when the control vgrid'ofy a separated function gas .tube is.

made negativeiwith` respectto the main'cathode thereof, currentfwill flow. to the controlgrid. It

should be' notedithat this current' is notanielectron current; but ratheraris'es" from? the.4 flow of positive ions to the controlfgridau As is shownbythe curve of Fig. 3, the relationbetween ygrid- Y current and grid voltageis quite nonlinear; with thedegree of nonlinearityv increasing somewhat as the grid-voltage approaches zerohfrom the negative direction. l A comparisonofFigs.r2and 3 will show thatboth curves have morenoniir-iearity:

in the region between -l'arid 4zero thanA in the region between v-25 and-10. Thusfthfecurvature of the` two curves is 'sufficiently similar to permit combination` thereof'in-suitable circuits t providev a linearizingactioninthe operation of aseparfated function fgas tube;

For example, there'is shownin Fig. fthecire cuit diagram of a separatedvfuiiction"gas tube' system embodyingthe'ggeneral principles" ofitheprises a gas tubeilfhaving.electrodes "I-2"-'22 adapted to ,be 'connected-through a pair of input f terminals 35- in series with a bias voltage source,

shown asav battery 34, anda'high impedancey element v3B, between the-control-grid I4= and :the--` maincathode I2; j l

Inwoperation, the voltage source-'34.wi1l estab- This current will b'esubstantially linearly related to theivoltage 'variations arisingi from the `signal.

sour-ce 32. However; itis yevident from considera- Y tion 'of' the .curvedlcharact'eristic shownin IFigL, 3 that the grid-voltage will not be linearly related tothe output lof thesigral source. Ratheiiit will have la'. nonlinear? relation corresponding: to" the' curve 'ofFig' 3. Accordingly, the load circuit4 current Vwill -benp'iuch. more? linearly related tothef signal voltage than wouldbe thecase iflthef high impedance se; wereV lcliminatecifrr'om Y the :circuiti IV Fig. 5, a circuitiillustrating.theforegoinge principlev is shown -inf' nic'ie'fspecic form: In 4thef` circuit of Fig. 5, a separated function-igastube I0 isconnected as an amplifyingelement between asignal source, comprisirfig a phonograph pickup 32o i,and y a loadI shown `as af lou'd'spealler-i24d; The voice coil A215 of theV loudspeaker 241flis5cnected between the operating voltage-source 26 andthe gasitube anode I6-. The inptjcircuit -for apply-ing', 4the signal" freni 'the' phonograph pickp egitto the icucispsaires outputftbe:` n comprises av triode vacuum 'ftub'e' 36u.' Thetriodeand ff is connected directly to the gas tube controlgrid It; The tr-iode cathode 40 5 is connected through a `bias'network 42 'andavcltag 's-urcef' gasjf tubegmain cathode* l2." The* trios lcontrol;

e grid ',4`4is conrnected through? a coupling-capacitor tri'ode 36a 'effectively` .comprises fa: variable high impedance in series with the voltage source` 34Y betwenthe gas tube 'control grid `Hi and main cathode' l2. The voltage source. 34 providesboth bias voltage for the gas tube I and operating voltage for the triode 36a. Assuming that the triode 36a is operated on the linearportion oi its characteristic, thenthe Avoltage at the gastube control grid I4 will be nonlinearl'y related to the pickup output signal, in accordance with the curve shown inF'ig. Bandas already described generally' in connection with Fig. 4.

At iirst glance, it might seem that the circuit. of Fig. 5 is not essentially different from similar'V separated function.gasxtube'circuits such as are shown, Vfor exampleQin the copending application of E. O. Johnson, SerialNo. 203,948, filed JanuaryY 2, 1951, and assigned to the assigneeA of the presentinvention. However, inthe circuitsshown in the last-mentioned YJohnson application; wherein avacuum tube comprises part of the input circuit Orla' separated function gas tube, Ythe grid-l cathode space of the gas tube is inshunt with the vacuum tube, rather than inseries with the triode and its operating voltage source 34 as in the circuit of Fig. 5. The shunt arrangement involves the following difficulties where linearity of the gas tube output is important:A

In order for the vacuum tube Vto havea linearizing effect, it is essential to have a.Y relatively large load impedance connected between the vacuum tube anode and the operating voltage source. Otherwise, Ythe vacuum tube will not present the required high impedance in the gridmain cathode circuit of the gas tube. On the other hand, if a'large ranode load impedance is used, then it becomes dinicult to operate the vacuum tube atall, and a much larger operating voltage source is required. In the circuit ,of Fig. 5, by comparison, the operating voltageY source for the vacuum tube 36a is in series with the gridmain cathode space of the gas tube and therefore does not involve theanode load impedance'y problem just mentioned.

l In Fig. 6 there isA shown a curve relating thev triode grid-cathode voltageto load current for a circuit of the type shown in Fig. 5. It canbe seen that such a circuit provides a linear, inputoutput relation for load currents between approximately SOand 160 ma.

By using a multigrid tube in the gas tube input circuit,.the 'relations `shown in Fig. A6 canA be caused to shift so that linear operation is .ob-

tained at different values of gas tube load current.V This occurs because operation is extended intonthe nonlinear region of the vacuum tube Whose characteristic is determined vby theauir-y iliary grid voltage. In other Words, by suitably adjusting the voltage on auxiliary grids inthe vacuum tube, thev region of linear operation of thema. to 120; from 50 to 130, etc.

In order to increase the extent of the linear operation region on the curve of Fig. 6, it becomes necessary to use a suitable nonlinear impedance element in the gas tube input circuit.

The current-voltage curve that the nonlinear impedance elementfshouldghav for ny .given case ca'nfbe determined by assuming specific values of input voltage, lVi, and gas .tube anode. current Ia, to obtainanexpression relating these.;

two parameters. Input voltage *.Vi is here 'taken to mean the vtotal voltage in the gridcathodecir--.

cuit lof thegas tube; in Fig. 4, for example,the instantaneoussumi of .rthevoltages of the battery 34.and the signal source. 32. Fro1n.theA curves of Figs. 2 and 3, one then can ,obtain a. table'of the valuesk of current-voltage. relationshiprequired;

. For xamplegitwouldbe reasonable to havela situation vinwhich anode current Insisto-vary from y.260. ma.` at zero` input voltage Vrto 20 ma.v for 40 input volts. This could :be expressed asi.

'i v*'Ihevvoltage across the impedance would be related to the inputvoltagevi and the gasrtubev grid-tofcathode voltage ,Vg Vby the expression: 2) vizvi-V-g From equations v(1) and (2),'and the curves of Figs. 2 and 3, thelfollowing table can be de- From Table I, the'values of VX and'I-g-canl be used to plot the current-Voltage curvethat anone linear impedancefelem'ent must have to satisfy the linearity requirements ofthe system'. Such a curve is plotted in'Fig. 8;

onenonlmear'eierent that wiupfovidea criar-v acteristicv very sim'ilar tothatfshown in Fig: 8 is ari inversely operated germanium crystal rectie'r. That`is,'ifvoltag'e isapplied across a rectie` fier of this type inadirection such asto cause current to ilow inverselyv through the rectifier, the current-volta'gefrelation will be substantially as shown'in Fig.8.j v j A gas tube/input circuit utilizingja germanium crystal rectifier is shown in Fig. 9wherein" the input circuit 4for' va separated function gasv tube I comprises the series combination 'of a germanium crystal rectifier 36e, a signal source 32,' and a bias voltage source 34. Due to the nonlinear impedance presented by the rectifier 36o to the ow of `grid current therethrough, a much'more eective linearization of the gas tube output current can be obtained.

Other Ynonlinear impedance l:elements similarly can be used in the gas tube input circuitto im-fVv prove linearization. For example, asis 'shown' 11;'a` transistor 36dis, shown connected in the signal input? circuit of aseparated function gas. tubeel to obtain linearizing action. .Thetransisf toncollectorGD .is connectedto 'the gas tube .conf y trolgridzM;A The transistor base 62 iisconnected: throughv aisig-nalisource E32 and .operating voltagesource 3,4toth`efgas tube main cathode. I2. The

transistor emitter. y(ill is connected Ifthrougha :curl rent limiting vresistor 662 andbias voltage: source S8f. to.. the. base 62'. With. this arrangement, .then

collectorato,-base` circuit'of. the transistor 36e will comprise a nonlinear variable impedance inthe gridm'ain.- cathodecircuitoffthegas. tube l0.

Variation:I ofthe-.emitter biasxprovided. by thesource v.lficaiL-be.-utilizeclto alterfor shape the'vv circuit. characteristic.-

From the foregoing, itY can be seen that the present invention provides a variety of simple and eilicientarrangements for obtaining a linear relationb'etween signal source` voltage andzoutputi current-in aseparated function gas tube circuit;

-What is elaimedis:

1. In a circuit for controlling in accordance wtha signal voltage the main cathode-anode current of agasfiilled'electron tube of the type having an anode, a main cathode, a controlgrid" higli impedance element' comprises av vacuumV tube having an anode electrode connected to' said gas tube control grid and havingja controlelectrodeconnected to receive said signal voltage.

5`. A circuit as dcnedin' claimA 1 whereinv said high. impedance element comprisesv asemiconductor element, said semiconductor element hav-v ingafrst electrode connected to said gas tube control grid and having. a second electrodecon'f nectedto said gas tube cathode, andimeans to applysaid signal .voltage in series with said'sec-L o nd electrodeand said'V gas tube cathode.

' 6'. In' a" circuit for operatinga gas iillede'elec-n tron tube of the 'type' having ananode, acathode;

a controlv electrode' therebetween,V and an aux#A iliary electrode cooperable'with one of sa-idr elec# trod'es for passing ionizing. currentthrough the tube gas,y the' combination of4 a signal voltageY source; a unidirectional voltage source, -a high impedance element, anda circuit:connectingsaidl voltage sources and said in'iptedanceelem-ent in'- series' between said ,mainV cathode and sadrcom trolelectrode Y 8i L75.: In` a, .circuit for operating. a gas filled electron. tube..of the. type having an anode; a cathodef,: af: control electrode therebetween', and anauxiliary electrodevcooperable with one of said'electrodesf forpassing ionizing. current through th'e .tube gas.

the'. combination of ;v a .high impedancev element;

connected to said: control. electrode, and means.

to apply. across theseries combination` ofA said; impedance andthe space path betweensaid conf.-

trol electrode andsaid .cathode .a signalpvoltage"v control electrodev th'erebetweemand l,an auxiliary, electrodevoooperable.with oneof saidelectrodesiv for passing,ionizingcurrent through.thetube.gas; the combination .ofsavariable impedance .elementi connected to said control electrode, a voltage'. source connecting said impedance inzseries with.` the. space path vbetween said control electrode and".

said cathode, and meansto vary the impedance:V of isaidv variable impedance. element in accordance.

tron tube. of' thetype havinga plurality: of elec:- :r

trodes including afirstpair. of electrodesooop-y erablezto pass .ionizing current throughthe .gasf in said tube, a.. second pair of electrodes*.forpassa-Y ingcurrent through the ionizedgas, and ancona trolLelectrode. between .said last named electrode;

pair. for.controlling said last named. current, .the'f combination of a` source of voltage, .animpedance element, a, circuit connecting said sourceandjsaid' impedance. in series between vsaid .control electrode and one of-said last named pairof elece trodes,..and means to vary. the currentflovving.y through'. said last named circuit in accordance?. with a signal voltage to be amplied. .v Y 12. A-gas tube circuit comprising a gasglled.; electron tube lhaving a main cathode'electrode, an.. anode: electrode, an electrode' for controlling currentnowvbetweenl said main cathode and,2 anode.l and an auxiliary cathode fromwhich? ionizingcurrent can be drawn to one of ysaid elec: trodes,. afrst voltage source, means .connecting said. main cathode and said auxiliary cathodeV across. said voltage source, 3,. second voltage.;

No referencesfcited. 

